Landmark Completion of South Pole Telescope.

Here to Help Scientists Learn What the Universe Is Made of and How it Got Here

February 26, 2007

A new South Pole telescope took its first glimpses on Feb. 16, 2007. Credit: National Science Foundation

Soon, a far more distant quarry will enter the South Pole telescope's (SPT) sights, as a team of researchers from nine institutions tackles fundamental mysteries of modern cosmology and the nature of the universe: What, for example, is dark energy, the force that dominates the universe?

The $19.2 million telescope is funded primarily by the National Science Foundation (NSF), with additional support from the Kavli Foundation of Oxnard, Calif., and the Gordon and Betty Moore Foundation of San Francisco.

"The telescope, camera and optics are all working as designed," said John Carlstrom, the S. Chandrasekhar distinguished service professor in astronomy and astrophysics at the University of Chicago, who heads the SPT team that tested the scope on Feb. 26. "SPT's first light is a major milestone for the project and a fitting conclusion to a remarkably productive summer at the South Pole station. We now look forward to fully characterizing the instrument and beginning cosmological observations."

"First light" is the scientific term for the time when a telescope becomes operational.

The telescope stands 75 feet (22.8 meters) tall, measures 33 feet (10 meters) across and weighs 280 tons (254 metric tons). It was assembled in Kilgore, Texas, then taken apart, shipped across the Pacific Ocean to New Zealand, and flown from there to the South Pole. Since November, the SPT team under the guidance of project manager Steve Padin has worked furiously to reassemble and deploy the telescope.

As with any construction project at the Earth southern extremity, SPT was supported by a long and complex logistical chain stretching around the globe. All cargo to the South Pole is delivered by ski-equipped LC-130 aircraft, and the components must be able to be broken down to fit into the aircraft cargo bay. Flown by the N.Y. Air National Guard, the aircraft are elements of Operation Deep Freeze, the military support arm of the U.S. Antarctic Program, which also includes Air Force cargo jets and U.S. Coast Guard icebreakers, Navy cargo handlers and many other logistical and personnel assets.

Raytheon Polar Services Co, of Centennial, Colo. is NSF's logistics contractor in Antarctica. RPSC personnel played a variety of essential roles in the successful completion of the SPT project, NSF officials noted.

Astrophysicists know that the universe has been expanding since the Big Bang occurred 13.8 billion years ago. In the late 1990s, astronomers using exploding stars as cosmic tape measures discovered that the expansion of the universe is accelerating. This led them to the idea that dark energy pushes the universe apart, overwhelming gravity, the attractive force exerted by all matter in the universe.

"We would like to know what makes the universe evolve," said Stephan Meyer, professor in Astronomy & Astrophysics at the University of Chicago.

An Important Anniversary and a Historic Achievement

SPT's first views occurred almost exactly 50 years after a team of 18 men spent the first winter in history at the South Pole as part of the 1956-1957 International Geophysical Year (IGY). They occurred just days before nations around the globe launched the International Polar Year 2007-2008, the first such global research campaign since IGY. The U.S. opening ceremony for IPY was held today at the National Academies of Sciences in Washington D.C.

Under the joint leadership of scientists Paul Siple and Navy Lt. John Tuck, 18 men were first to spend the winter at the pole in a station the U.S. Navy built in the austral summer of 1956-1957, using cargo dropped by U.S. Air Force planes. Siple, Tuck and the 16 other "winterovers" were also the first people in history to witness sunset and sunrise at the South Pole, events that are separated in Antarctica by six months of darkness and frigid cold. On Sept. 18, 1957, in the depths of the austral winter, temperature at the station dropped to -107 degrees Fahrenheit (-77.2 degrees Celsius), the coldest temperature recorded on Earth at the time.

"We were like men who had been fired off in rockets to take up life on another planet. We were in a lifeless and almost featureless world. However snug and comfortable we might make ourselves, we could not escape from our isolation," wrote Siple in his memoir, Living at the Pole. "We were now face to face with raw nature so grim and stark, that our lives could be snuffed out in a matter of minutes. Every day would bring us new problems to solve and our ingenuity would be taxed over and over again. And all this to carry out a somewhat difficult fragment of the worldwide scientific program of the International Geophysical Year."

The men laid the foundation for the scientific legacy that continues into the 21st Century, as NSF completes construction of the third permanent station at the South Pole.

The South Pole: A Premier Observatory

Astronomers work at the South Pole to take advantage of excellent viewing conditions. Cold, dry Antarctica will allow SPT to more easily detect the cosmic microwave background (CMB) radiation, the afterglow of the big bang, with minimal interference from water vapor. On the electromagnetic spectrum, the CMB falls somewhere between heat radiation and radio waves.

The CMB is largely uniform, but it contains tiny ripples of varying density and temperature. These ripples reflect the seeds that, through gravitational attraction, grew into the galaxies and galaxy clusters visible to astronomers today. The SPT's first key science project will be to study small variations in the CMB to determine if dark energy began to affect the formation of galaxy clusters by fighting against gravity over the past few billion years.

Galaxy clusters are groups of galaxies, the largest celestial bodies that gravity can hold together. "Our galaxy, the Milky Way, is in one of these clusters," Meyer said. "And these clusters of galaxies actually change with time."

The CMB allows astronomers to take snapshots of the infant universe, when it was only 400,000 years old. No stars or galaxies had yet formed. If dark energy changed the way the universe expanded, it would have left its "fingerprints" in the way it forced galaxies apart over the deep history of time. Different causes would produce a different pattern in the formation of galaxy clusters.

According to one idea, dark energy could be Albert Einstein's cosmological constant: a steady force of nature operating at all times and in all places. Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of the day. If Einstein's idea is correct, scientists will find that dark energy was much less influential in the universe 5 billion years ago than it is today.

"Clusters weren't around in the early universe. They took a long time to evolve," Carlstrom said.

Another version of the dark energy theory, called quintessence, suggests a force that varies in time and space. Some scientists even suggest there is no dark energy at all, and that gravity merely breaks down on vast intergalactic scales.

To pinpoint when dark energy became important, SPT will use a phenomenon called the Sunyaev-Zeldovich effect, which distorts the CMB as it passes through the hot gas of intervening galaxy clusters. As the microwaves interact with gas in the clusters, some of the microwaves get kicked into a higher frequency. SPT will measure the slight temperature difference associated with the frequency change and produce an image of the gas in the cluster.

SPT can scan large regions of the sky quickly. Scientists expect it to detect thousands, or even tens of thousands, of galaxy clusters within a few years. "To get a meaningful constraint on dark energy through measuring galaxy clusters, you need something like this South Pole Telescope," Carlstrom said. "The cluster SZ [Sunyaev-Zeldovich] signals cover small patches in the sky relative to the intrinsic variations in the cosmic microwave background. To get the necessary resolution, you need a big telescope. Now we have one."

Senior members of the SPT team include William Holzapfel, Adrian Lee and Helmuth Spieler from the University of California at Berkeley and the Lawrence Berkeley National Laborator; Joe Mohr, from the University of Illinois at Urbana-Champaign; John Ruhl from Case Western Reserve University; Antony Stark, from the Harvard-Smithsonian Astrophysical Observatory; Matt Dobbs from McGill University; and Erik Leitch of NASA's Jet Propulsion Laboratory.

Source / Credit: NSF